Semiconductor device

ABSTRACT

A semiconductor device includes: a plurality of semiconductor chips spaced apart from one another; and a conductive part. The plurality of semiconductor chips include respective semiconductor switching elements. The conductive part connects the plurality of semiconductor chips in parallel. A material of the semiconductor switching elements of the plurality of semiconductor chips includes a wide bandgap semiconductor. At least one of the semiconductor switching elements has a channel length of 1.5 μm or less.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to semiconductor devices.

Description of the Background Art

A semiconductor switching element including a wide bandgapsemiconductor, such as silicon carbide (SiC), as a material thereof hasrecently been proposed (e.g., International Publication No.2016/147243).

In a semiconductor device in which a plurality of semiconductorswitching elements including a wide bandgap semiconductor as a materialthereof are connected in parallel, the phenomenon of signal oscillationis likely to occur not only during steady state operation but alsoduring startup and short circuit operation. The phenomenon ofoscillation becomes noticeable particularly in a configuration in whichsemiconductor chips are connected in parallel.

SUMMARY

The present disclosure has been conceived in view of a problem asdescribed above, and it is an object of the present disclosure toprovide technology enabling suppression of the phenomenon ofoscillation.

A semiconductor device according to the present disclosure includes: aplurality of semiconductor chips including respective semiconductorswitching elements and spaced apart from one another; and a conductivepart connecting the plurality of semiconductor chips in parallel. Amaterial of the semiconductor switching elements includes a wide bandgapsemiconductor, and at least one of the semiconductor switching elementshas a channel length of 1.5 μm or less.

The phenomenon of oscillation can be suppressed.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a configuration of a semiconductor deviceaccording to Embodiment 1;

FIG. 2 is a cross-sectional view showing a configuration of asemiconductor switching element according to Embodiment 1;

FIG. 3 is a plan view showing a configuration of a semiconductorswitching element according to Embodiment 2;

FIG. 4 is a plan view showing a configuration of a semiconductorswitching element according to a modification of Embodiment 2; and

FIG. 5 is a circuit diagram showing a configuration of a semiconductordevice according to Embodiment 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments will be described below with reference to the accompanyingdrawings. Features described in the embodiments below are examples, andall the features are not necessarily required. In description madebelow, similar components in the embodiments bear the same or similarreference signs, and different components will mainly be described. Indescription made below, specific locations and directions represented byterms such as “upper”, “lower”, “left”, “right”, “front”, and “back” maynot necessarily match locations and directions in actual implementation.A higher concentration in a portion than in another portion means thatan average concentration in the portion is higher than an averageconcentration in the other portion, for example. In contrast, a lowerconcentration in a portion than in another portion means that an averageconcentration in the portion is lower than an average concentration inthe other portion, for example.

Embodiment 1

FIG. 1 is a plan view showing a configuration of a semiconductor deviceaccording to Embodiment 1. The semiconductor device in FIG. 1 includesan insulating substrate 1, circuit patterns 2 and 3, a plurality ofsemiconductor chips 4 and 5, wires 6 and 7, and a gate terminal 8.

The circuit patterns 2 and 3 are spaced apart from each other, and areselectively arranged on the insulating substrate 1. A material of thecircuit patterns 2 and 3 is metal, such as copper.

The plurality of semiconductor chips 4 are spaced apart from oneanother, and are selectively arranged on the circuit pattern 2. Thesemiconductor chips 4 include respective semiconductor switchingelements, such as metal oxide semiconductor field effect transistors(MOSFETs), insulated gate bipolar transistors (IGBTs), and reverseconducting-IGBTs (RC-IGBTs), and the semiconductor switching elementseach include a gate electrode 4 a and a source electrode 4 b insulatedfrom each other. The semiconductor switching elements may be planarsemiconductor switching elements or may be trench semiconductorswitching elements. The number of semiconductor chips 4 is not limitedto eight as shown in an example of FIG. 1 , and is only required to betwo or more.

A material of the semiconductor switching elements of the semiconductorchips 4 includes a wide bandgap semiconductor. Examples of the widebandgap semiconductor include silicon carbide (SiC), gallium nitride(GaN), and diamond. The semiconductor switching elements made of thewide bandgap semiconductor are capable of stable operation at a hightemperature and a high voltage and faster switching speed compared withthe semiconductor switching elements made of silicon.

The semiconductor chips 5 are spaced apart from the plurality ofsemiconductor chips 4, and are selectively arranged on the circuitpattern 2. The semiconductor chips 5 each include a diode, such as a PNjunction diode (PND) and a Schottky barrier diode (SBD). A material ofthe diode of each of the semiconductor chips 5 may include the widebandgap semiconductor as with the material of the semiconductorswitching elements of the semiconductor chips 4.

The circuit pattern 2 and drain electrodes of the semiconductor chips 4are connected, and the circuit pattern 2 has a function of a drainterminal. The wires 6 connect source electrodes 4 b of the semiconductorchips 4, connect the semiconductor chips 4 and the semiconductor chips5, and connect the semiconductor chips 5 and the circuit pattern 3. Dueto this connection, the circuit pattern 3 has a function of a sourceterminal. The wires 7 connect gate electrodes 4 a of the semiconductorchips 4 and the gate terminal 8. A material of the wires 6 and 7 isaluminum, for example. Instead of using the wires 6 and 7 for thesemiconductor chips 4 and 5, direct lead bonding may be used to connectleads to the semiconductor chips 4 and 5.

A conductive part according to Embodiment 1 includes the circuitpatterns 2 and 3 and the wires 6 as described above, and connects theplurality of semiconductor chips 4 in parallel. In the example of FIG. 1, four columns of semiconductor chips 4 are connected in parallel by thecircuit patterns 2 and 3 and the wires 6.

FIG. 2 is a cross-sectional view showing a configuration of each of thesemiconductor switching elements of the semiconductor chips 4. Anexample in which the semiconductor switching element is a MOSFET will bedescribed below.

The semiconductor switching element in FIG. 2 includes the gateelectrode 4 a, the source electrode 4 b, a drain electrode 4 c, an n⁻layer 11, a p layer 12, n⁺ layers 13 and 14, and an insulating layer 15.The n⁺ layers 13 and 14 have a higher n-type impurity concentration thanthe n⁻ layer 11. The n-type and the p-type of these components in FIG. 2may be reversed.

The p layer 12 is selectively disposed in an upper portion of the n⁻layer 11, and the n⁺ layer 13 is selectively disposed in an upperportion of the p layer 12. The gate electrode 4 a is disposed over aportion of the p layer 12 located between the n⁻ layer 11 and the n⁺layer 13 via the insulating layer 15. The insulating layer 15 has anopening exposing a portion of the p layer 12 and a portion of the n⁺layer 13, and the source electrode 4 b is electrically connected to thep layer 12 and the n⁺ layer 13 via the opening. The n⁺ layer 14 isdisposed in a lower portion of the n⁻ layer 11, and the drain electrode4 c is disposed in a lower portion of the n⁺ layer 14.

When a gate voltage greater than a threshold voltage is applied to thegate electrode 4 a, the type of the p layer 12 close to the gateelectrode 4 a is reversed to the n-type to form a channel to allow acurrent to flow between the n⁻ layer 11 and the n⁺ layer 13. A channellength L is the length of the channel, and corresponds to the distancebetween the n⁻ layer 11 and the n⁺ layer 13 sandwiching the p layer 12.In Embodiment 1, at least one of the semiconductor switching elementshas a channel length L of 1.5 μm or less. The channel length L can bemeasured by a scanning transmission electron microscope (STEM),secondary ion mass spectrometry (SIMS), and the like.

<Summary of Embodiment 1>

The semiconductor switching element, such as a MOSFET, is typicallylikely to be in a pinched off state, that is, a state in which thechannel is closed to make a current less likely to flow, when a currentincreases during short circuit and the like. In Embodiment 1, theplurality of semiconductor chips 4 spaced apart from one another areconnected in parallel by the circuit patterns 2 and 3 and the wires 6,and at least one of the semiconductor switching elements of theplurality of semiconductor chips 4 has a channel length L of 1.5 μm orless. The channel length L is relatively short, so that drain resistancecan be reduced to mitigate the pinched off state. Since the channellength L is relatively short, parasitic capacitance of a gate can bereduced.

As a result, the phenomenon of oscillation of the semiconductorswitching elements of the semiconductor chips 4 can be suppressed, andthus improvement in reliability of the semiconductor device can beexpected. The inventors have found that, in a configuration in which thematerial of the semiconductor switching elements includes the widebandgap semiconductor, the effect of suppressing the phenomenon ofoscillation when the channel length L is 1.5 μm is more noticeable thanthe effect of suppressing the phenomenon of oscillation when the channellength L is 1.6 μm. When the number of columns of semiconductor chips 4connected in parallel exceeds three, it is practically difficult tosuppress the phenomenon of oscillation by matching circuit lengths, suchas the lengths of the wires 6, so that the above-mentioned effect isparticularly useful.

<Modification>

The wires 6 may connect the circuit pattern 2 and any of the pluralityof semiconductor chips 4, and the wires 6 may each have a length of 5 mmor more. Since the channel length L is relatively short, the phenomenonof oscillation of the semiconductor switching elements of thesemiconductor chips 4 can be suppressed even when the wires 6 each havea length of 5 mm or more. The wires 6 each having a length of 5 mm ormore allow tolerance to design relating to electrical insulation. Thepresent modification may be applied to configurations in and afterEmbodiment 2.

Embodiment 2

FIG. 3 is a plan view showing a configuration of a portion of asemiconductor device according to Embodiment 2, and specifically shows aconfiguration of a semiconductor switching element of a semiconductorchip 4 according to Embodiment 2.

The semiconductor switching element in FIG. 3 includes a terminationstructure 4 d in addition to the gate electrode 4 a and the sourceelectrode 4 b described above. The area of the gate electrode 4 a andthe source electrode 4 b is also referred to as an effective currentcarrying area. The termination structure 4 d is a guard ring, forexample, and surrounds the gate electrode 4 a and the source electrode 4b.

In Embodiment 2, at least one of the semiconductor switching elementsincludes the termination structure 4 d having a width D1 of 1 mm ormore, and at least one of the semiconductor switching elements has abreakdown voltage of 2.0 kV or more. A configuration other than theabove-mentioned configuration is similar to that in Embodiment 1.

An increase in width D1 of the termination structure 4 d of thesemiconductor switching element typically increases the breakdownvoltage of the semiconductor switching element, but increases the sizeof the semiconductor chip 4. The increase in size of the semiconductorchip 4 naturally increases the lengths of the wires 6 connecting thesemiconductor chips 4 to make the phenomenon of oscillation of thesemiconductor switching elements of the semiconductor chips 4 morelikely to occur.

According to Embodiment 2, however, the channel length L is relativelyshort as in Embodiment 1, so that the phenomenon of oscillation of thesemiconductor switching elements of the semiconductor chips 4 can besuppressed. As a result, a semiconductor device capable of high speedoperation while suppressing the phenomenon of oscillation even whenhaving a relatively high breakdown voltage can be achieved.

<Modification>

FIG. 4 is a plan view showing a configuration of a portion of asemiconductor device according to a modification of Embodiment 2, andspecifically shows a configuration of a semiconductor switching elementof a semiconductor chip 4 according to the modification.

As shown in FIG. 4 , with respect to at least one of the plurality ofsemiconductor chips 4, the semiconductor chip 4 may have a side lengthD2 equal to or greater than three times the width D1 of the terminationstructure 4 d of a semiconductor switching element of the semiconductorchip 4. According to such a configuration, a semiconductor devicecapable of high speed operation while suppressing the phenomenon ofoscillation can be achieved as in Embodiment 2.

Embodiment 3

FIG. 5 is a circuit diagram showing a configuration of a semiconductordevice according to Embodiment 3. In FIG. 5 , three semiconductor chips4 are connected in parallel.

At least one of the semiconductor chips 4 in FIG. 5 includes asemiconductor switching element 4 f, a body diode 4 g, and afreewheeling diode 4 h. The semiconductor switching element 4 f issimilar to each of the semiconductor switching elements described inEmbodiment 1. The body diode 4 g is a diode intrinsically formed by a pnjunction of the semiconductor switching element 4 f. The freewheelingdiode 4 h is connected to the semiconductor switching element 4 f. Thefreewheeling diode 4 h is not the body diode 4 g, and is separatelydisposed in a semiconductor substrate that is the same as thesemiconductor substrate in which the semiconductor switching element 4 fis disposed, that is, a semiconductor chip 4 that is the same as thesemiconductor chip 4 in which the semiconductor switching element 4 f isdisposed. A configuration other than the above-mentioned configurationis similar to that in Embodiment 1.

According to a configuration according to Embodiment 3 as describedabove, the freewheeling diode 4 h built in the semiconductor chip 4 thatis the same as the semiconductor chip 4 in which the semiconductorswitching element 4 f is disposed can perform freewheeling operation.This eliminates the need to mount another semiconductor chip, such asthe semiconductor chips 5 in FIG. 1 , allowing for reduction in size ofthe semiconductor device. Due to omission of another semiconductor chip,component count can be reduced to suppress oscillation between thesemiconductor chips 4. The freewheeling diode 4 h can reduce use of thebody diode 4 g, so that property deterioration of the body diode 4 g canbe suppressed to increase lifetime of the semiconductor device.

Embodiments and modifications can freely be combined with each other,and can be modified or omitted as appropriate.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

What is claimed is:
 1. A semiconductor device comprising: a plurality ofsemiconductor chips including respective semiconductor switchingelements and spaced apart from one another; and a conductive partconnecting the plurality of semiconductor chips in parallel, wherein amaterial of the semiconductor switching elements comprises a widebandgap semiconductor, and at least one of the semiconductor switchingelements has a channel length of 1.5 μm or less.
 2. The semiconductordevice according to claim 1, wherein at least one of the semiconductorswitching elements includes a termination structure having a width of 1mm or more.
 3. The semiconductor device according to claim 1, wherein atleast one of the semiconductor switching elements has a breakdownvoltage of 2.0 kV or more.
 4. The semiconductor device according toclaim 1, wherein at least one of the plurality of semiconductor chipsfurther includes a freewheeling diode that is not a body diode of eachof the semiconductor switching elements.
 5. The semiconductor deviceaccording to claim 1, wherein with respect to at least one of theplurality of semiconductor chips, the semiconductor chip has a sidelength equal to or greater than three times a width of a terminationstructure of one of the semiconductor switching elements of thesemiconductor chip.
 6. The semiconductor device according to claim 1,wherein the conductive part includes: a circuit pattern; and a wireconnecting any of the plurality of semiconductor chips and the circuitpattern, and having a length of 5 mm or more.